Nucleic acid hybridizations are commonly used in biochemical research and diagnostic assays. Generally a single stranded analyte nucleic acid is hybridized to labeled nucleic acid probe, and resulting nucleic acid duplexes are detected. Radioactive and nonradioactive labels have been used. Methods also have been developed to amplify the signal that is detected. For example, large comb-type branched polynucleotides, comprising a first oligonucleotide unit and branches including second oligonucleotide units, have been developed for signal amplification in nucleic acid detection assays. In this application, the branched polynucleotide is hybridized via the first oligonucleotide unit to single stranded analyte nucleic acid and then labeled oligonucleotide is hybridized to the branched polynucleotide via the second oligonucleotide units, as described in U.S. Pat. No. 5,710,264 to Chiron Corporation.
Dendrimers have been developed that are assembled by the sequential hybridization of single DNA strands. Pairwise hybridization of single strands produces monomers with a double stranded center and four single stranded "arms". The monomers can be grown exponentially in sequential hybridization steps, to produce a macromolecule including terminal single stranded arms. The dendrimers may range in size from hundreds to millions of bases. The arms that are not to be hybridized to target can be hybridized to covalently labeled oligonucleotide. These dendrimers are commerically available from Polyprobe, Bala Cynwyd, Pa. Dendrimers for assaying nucleic acids are described in U.S. Pat. Nos. 5,175,270, 5,487,973, and 5,484,904, the disclosures of which are incorporated herein.
Avidin-biotin systems have been developed for use in a variety of detection assays. Methods for the detection and labeling of nucleic acids in biotin systems are described, for example, in "Nonradioactive Labeling and Detection Systems", C. Kessler, Ed., Springer-Verlag, New York, 1992, pp. 70-99; and in "Methods in Nonradioactive Detection,", G. Howard, Ed., Appleton and Lange, Norwalk, Conn. 1993, pp. 11-27 and 137-150.
Methods for the detection of nucleic acid sequences have suffered from drawbacks including background noise, time and labor requirements, lack of specificity and lack of sensitivity. It is an object of the invention to provide materials for the detection of polymers, particularly nucleic acids. It is a particular object of the invention to provide methods and compounds for amplifying labeling signals used in the detection of nucleic acid sequences in specific binding assays. It is a further object of the invention to provide methods and compounds which permit nucleic acid sequences to be detected specifically and rapidly with high sensitivity and high resolution.